Disable HTTP/2 (#4)

We use [connect-go](https://github.com/bufbuild/connect-go) instead of [grpc-go](https://github.com/grpc/grpc-go) because connect-go support HTTP/1.1, that means we can mount the gRPC api on the Gitea server without change the protocol.

So it doesn't make sense that make the runner support both HTTP/1.1 and HTTP/2, and [upgrade the protocol used on Gitea](
https://github.com/wolfogre/gitea/blob/ae018b6b4864dfb5528df276755167be27b13148/modules/graceful/server_http.go#L23) to support HTTP/2 and h2c. Although it works right now, I believe there'll be lots of problems when the Gitea server is behind a reverse proxy.

So let's KISS, we don't touch the http protocol of Gitea, and disable HTTP/2 for runner. And we would support HTTP/2 in the future if we really need it.

Co-authored-by: Jason Song <i@wolfogre.com>
Reviewed-on: https://gitea.com/gitea/act_runner/pulls/4

config/config.go

@@ -23,10 +23,7 @@ type (
 	}
 
 	Client struct {
-		Address    string `ignored:"true"`
-		SkipVerify bool   `envconfig:"GITEA_RPC_SKIP_VERIFY"`
-		GRPC       bool   `envconfig:"GITEA_RPC_GRPC" default:"true"`
-		GRPCWeb    bool   `envconfig:"GITEA_RPC_GRPC_WEB"`
+		Address string `ignored:"true"`
 	}
 
 	Runner struct {